<h1>Fibonacci sequence</h1>
<label>Which number: <input type="number" #num></label>
<button (click)="updateMessage(num)">Calculate</button>
<h3 *ngIf="num.value !== '' && !error">{{num.value}}# fibonacci number is {{result}}</h3>
<h3 *ngIf="error">{{error}}</h3>
